The danger of exposure to chemical or biological agents can be severe. Whether a result of unintended release, by way of, e.g., an accident, or a result of intentional delivery, it is desirable to quickly and accurately identify (1) the type of agent that has been released and (2) the precise area of contamination. Early and accurate detection of such dangerous substances can be a significant factor in reducing potential casualties and limiting further spreading of the agent, e.g., by wind, human and animal contact, etc.
It is likewise important to be able to quickly and accurately identify the presence of explosive materials. Such detection is particularly important in security and military settings. The sooner detection can take place, the sooner personnel can be evacuated or other appropriate measures taken.
Prior remote sensor technologies designed to measure surface-deposited chemical contamination used vehicles and associated test equipment that retrieved a physical sample of the contaminant and then used an extremely cumbersome and time-consuming process to analyze the sample, e.g., a mechanical sampling wheel system coupled with a mass spectrometer to test for chemical agents.
In view of the complexity of such approaches, newer, simpler technologies were desired. One emerging technology in response to this desire is referred to, generally, as “standoff surface detection,” and refers to a category of technologies that permit detection of a substance without actually having to physically come in contact with the substance. The goal of these detection systems is to provide the capability to detect, identify, locate, quantify, warn, and report chemical and biological threats and thereby give military forces or civilian personnel sufficient early warning to avoid (further) contamination and deploy appropriate counter measures.
One of the technologies that enables standoff surface detection is Raman spectroscopy. Raman spectroscopy is a technique used to characterize materials and thereafter to identify such materials. Typically, a laser transmitter serves as a spectrally narrow light source with high irradiance. The laser illuminates a known or an unknown substance, such as a chemical compound, biological agent, or explosive material, among others. A portion of the incident light is Raman scattered by the substance. This light is scattered in all spatial directions as well as shifted spectrally to discrete wavelengths. These wavelength shifts correspond to unique vibrational energies associated with the molecular bonds in the substance.
In conventional standoff Raman spectroscopy systems, the Raman scattered light is collected by a telescope and is coupled into a dispersive optical system. The telescope focuses the collected light onto, e.g., an optical fiber bundle. At the opposite end of the fiber bundle, individual fibers are oriented linearly to form an entrance slit for a grating-based spectrograph. An electro-optical detector array records the optical spectrum of the Raman scattered light. This spectrum serves as a “fingerprint” for the known or unknown substance. An analysis computer stores the reference spectral information along with information identifying the known substance, and more often, employs pattern-matching algorithms to identify the unknown substance from a spectral library of previously analyzed and “fingerprinted” reference substances.
Laboratory-based Raman spectroscopy systems have been in use for many years. Recently, portable Raman systems have become possible as a result of components that have decreased in size and unique integration techniques. A description of one such portable system can be found in U.S. Pat. No. 6,608,677, which is incorporated herein by reference. A backpack implemented man-portable Raman sensor has also recently been fielded by ITT (Wilmington, Del.). Aspects of that system are described in U.S. Pat. No. 7,796,251, entitled Method, Apparatus and System for Rapid and Sensitive Standoff Detection of Surface Contaminants, which is also incorporated herein by reference. Truck mounted Raman sensors have also been fielded to date. Reference may also be made to U.S. Pat. No. 6,788,407, also incorporated herein by reference, for still further discussion of Raman spectrometry.
Notwithstanding these known systems, there remains a need to provide different forms of Raman sensors to meet the needs of both civilian and military personnel responsible for identifying, especially, trace amounts or residues of explosive substances.